The present work, which is the first comparative study of the growth of the fan mussel Pinna nobilis in the western Mediterranean, encompasses 12 populations of this species living in different environments in France and Spain. Two hundred nine shells were processed and used to obtain growth records from the posterior adductor muscle scar. Size-at-age data were fitted to the Von Bertalanffy growth model. Considerable variability in growth parameters and age was detected among the populations. The results show that the only two fan mussel populations remaining in Spain, which live in an estuary and a coastal lagoon, occupy habitats that are optimal for fast growth, but individuals show low longevity, complicating the long-term conservation of the species. Multivariate analyses groups the populations into three groups (SO, EO and LG), and a general model is proposed for each group; the model can be used as an approximation to calculate the ages of individuals living in similar environments.

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Background The measurement of the energy available for growth (scope of growth, SFG) can be used in bivalves to make a long-term prediction in a short-term experiment of the condition of the individual. In order to tackle the best conditions for captive maintenance of Mediterranean Pinnids, a SFG study was conducted using Pinna rudis as a model species. Three diets were examined to test the viability of live microalgae and commercial products: i) a control diet using 100% of live microalgae based on the species Isochrysis galbana (t-ISO), ii) a 100% of commercial microalgae diet based on the product Shellfish Diet 1800®, and iii) a 50/50% mix diet of I. galbana (t-ISO) and Shellfish Diet 1800®. Results SFG results showed significant differences among diets in the physiological functions measured and suggested lower acceptability and digestibility of the commercial product. Negative SFG values were obtained for the commercial diet which indicates that it should be rejected for both Pinnid maintenance. The mixed diet showed improved physiological performance compared to the commercial diet, resulting in a higher SFG that had no significant differences with the control diet. However, in the long-term, the lower digestibility of the mixed diet compared to the control diet could lead to a deterioration of individuals’ conditions and should be considered cautiously. Conclusions This work represents the first case study of SFG in Pinna spp. and provides fundamental data on dietary needs for the critically endangered species, P. nobilis.

The fan mussel Pinna nobilis is experiencing a mass mortality event throughout the Mediterranean Sea. The survival of the remaining isolated populations and the maintenance and reproduction of individuals in captivity could determine the future of the species. This paper examines the clearance rate (CR) and oxygen consumption (VO2) of fan mussel individuals measured under 5 different temperatures (8.5, 14, 18, 23 and 28ºC). The measurements of both physiological variables revealed a threshold limit of thermal tolerance at both extreme temperatures, indicating the critical situation of the remaining populations, which are located in coastal lagoons and shallow bays where these extreme temperatures usually occur. Besides, the high clearance rates observed highlight the significant ecosystem service provided by the species in terms of water filtration, especially in confined waters with low renewal rates. Routine control of the clearance rate as an early warning system is proposed for detecting ailing individuals. Such a system could also be used to improve captivity conditions.

The present study reports new knowledge into the biological rhythms of subtidal bivalves using the fan mussel Pinna nobilis as model. The objective was determining which factor(s) provoke the change between two different patterns observed in the annual cycle of this species: P1, characterized by the individuals opening and closing their valves following the presence and absence of ambient light and P2, characterised by a behaviour independent of the presence of light. Magnetoresistive sensors were installed on 8 fan mussels to record gaping activity in laboratory conditions. Different temperature and light treatments were applied. Results showed temperature as the factor modulating the change between behavioural patterns. The individuals switched to P1 when temperature reached 24.5º C. In this pattern, individuals are entrained by light showing a circadian rhythm linked to the daily light treatments. During P2, the circadian rhythm was missing or very weak, contrary to in situ observations. The results of the present study contribute to understand the biology of the species in order to plan new conservation strategies. Furthermore, the observed relationship between temperature and P1 is of interest to develop captive breeding of fan mussels. Altogether, this information is especially relevant in view of the recent mass mortality of P. nobilis occurred in the western Mediterranean.